Isopropyl acetate is a compound which is useful as a solvent or as a material for preparing perfumes.
It is known that isopropyl acetate can be prepared in a liquid phase reaction of acetic acid with propylene in the presence of an acidic ion-exchange resin catalyst [eg. Japanese Patent Unexamined Publication(Kokai) No. 169552/19923], through the following equation. EQU CH.sub.3 CHOOH+CH.sub.2 =CHCH.sub.3 .fwdarw.CH.sub.3 CHOOCH(CH.sub.3).sub.2
Furthermore, it is known that unreacted acetic acid is recirculated in an industrial process for the preparation of isopropyl acetate in order to increase the overall yield(eg. Hydrocarbon processing, Apr. 1975).
A hydrocarbon mixture containing above 20% by weight of propylene is preferably used in the industrial process for the preparation of isopropyl acetate as a starting propylene having impurities from the view point of cost.
The hydrocarbon mixture includes a distillate fraction having a carbon number of 3 which is obtained by catalytically cracking petroleums such as a naphtha or a crude propylene which is obtained as a by-product in a process for the preparation of isobutene by the dehydrogenation of isobutane, as the starting propylene having impurities.
However, in the case that the above-mentioned crude propylene is used, isopropyl alcohol(boiling point of 82.degree. C.), etc. are produced as a by-product in the reaction of propylene with small amounts of water which is contained in the starting crude propylene and acetic acid.
Small amounts of water is also inevitably produced with the generation of acetic anhydride from acetic acid.
Furthermore, olefins having a carbon number of 7 and acetates having a carbon number of above 6 are produced as by-products by the reaction of the impurities(olefins having a carbon number of 4) in the starting materials with propylene and acetic acid, respectively.
The by-products have boiling points that are close to those of isopropyl acetate and acetic acid, resulting in that there is difficult to separate by distillation.
Accordingly, conventional arrangements of continuous distillation columns would increase the cost of equipment due to the necessity of many plates in the distillation columns, which, if not used, would result in an increased loss of isopropyl acetate.
The above process has many problems and is, therefore, not practical as an industrial process.
Given these circumstances, there has been much demand for a process for the preparation of isopropyl acetate having a high purity using the above-mentioned crude propylene, and as a result of the studies performed by the present inventors, the present invention has been completed.